At its core, a modern evaporative cooler typically comprises a stack of thin parallel spaced-apart plates. The plates define alternating wet and dry air-flow passages. In the wet passages a “working” airstream passes over wetted surfaces, accepting and carrying away sensible heat as well as latent heat of evaporation, leaving evaporatively cooled wet surfaces. In the dry passages an initially warm airstream is cooled as heat is transferred by convective transfer from the airstream to the cooled plate surfaces and by conductive heat transfer through the plates. The temperature gradient between the airstreams on either side of the thin plates drives the flow of heat from dry passage side to wet passage side.
U.S. Pat. No. 8,636,269 teaches an evaporative heat exchanger formed of corrugated sheets of material, each sheet having one wettable surface and an opposed dry vapour-resistant surface. Sheets are stacked with wettable surfaces facing each other to form wet passages and dry surfaces facing each other to form dry passages between the sheets. Within the passages, air flow in the center of the passages tends to flows fastest, while air nearest the sheet surfaces flows slowest. Air is an insulator, so the layer of slow moving air directly adjacent the plates constitutes an obstruction to heat transfer. To overcome this barrier, turbulence is introduced into the flow. In accordance with the invention, the general direction of air flow is at an angle to the corrugations, and heat exchange between the wet and dry passages and evaporation within the wet passages can readily take place due to the intensity of mixing promoted by the diagonal flow across the corrugated construction. However, as turbulence increases, so does resistance to flow.
The present inventors developed a more compact, two-stage evaporative cooler as disclosed in PCT/AU2015/050528, assigned to the present assignee. The inventors discovered that when the spacing between the plates is greatly reduced and care is taken to ensure laminar flow rather than turbulent flow, good evaporative cooling and good heat exchange occurs, allowing the length of the passages to be reduced. And although thin passages have a greater resistance to flow (greater pressure drop per distance), as the passage length is reduced the pressure drop becomes manageable.
That is, by pushing air at high shear rates through passages having narrower spacing between plates—and shorter passages—the evaporative cooling system becomes not only compact in size, it also becomes efficient. The smaller cores made possible by this new concept are referred to herein as “micro-cores”.
However, as the sheet spacing becomes thinner, a problem arises in manufacturing. Small micro-cores must be connected to large air inlets and outlets. It becomes increasingly problematic to connect, in a commercial scale manufacturing process, the inlet and outlet manifolds to the smaller and smaller wet and dry flow passages.
Further, the conventional manufacturing method involves producing individual plates, stacking the individual plates, aligning the functional structures of the plates, and somehow bonding or fixing the plates to each other. This is time and labour intensive.
A manufacturing method is needed to economically and reliably manufacture “micro-core” heat exchanger or other compact heat exchanger cores on a commercial scale, and in particular using commercially available materials and manufacturing techniques.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
In this specification, a statement that an element may be “at least one of” a list of options is to be understood that the element may be any one of the listed options, or may be any combination of two or more of the listed options.